It has heretofore been proposed to provide utility power distribution systems with load shedding capability whereby loads may be selectively disconnected from the power system during periods of peak demand. Users may be provided with the option to select the threshold at which the load is to be disconnected from the power grid based upon utility power rate or other criteria. One purpose of such a system is to provide the user with the option of reducing utility costs during periods of peak demand, while at the same time reducing overall load on the power grid.
In load shedding systems heretofore proposed, the operator or user input capability tends to be unduly complex, and difficult for many business and residential customers. Furthermore, many schemes contemplate inclusion of these capabilities at the time of initial system set up, such as when a home or business facility is constructed, and are not well adapted for use in connection with existing systems and buildings. It is therefore a general object of the present invention to provide a load shed module that is well adapted for use in conjunction with existing buildings and power distribution systems, and that is inexpensive to implement. Another and related object of the present invention is to provide a load shed module of the described character in which the operator may readily select a desired load shed threshold, based upon electrical power rate information received from the utility supplier, without technically complex threshold selection input means. A further object of the present invention is to provide a load shed module of the described character that includes voltage, current phase angle and power monitoring capability, and that is adapted to transmit energy consumption and status information to the utility power supplier. Yet another object of the invention is to provide a load shed module of the described character that is adapted to respond to control signals from the utility power supplier to shed or disconnect the associated load independent of the load shed threshold selected by the user.
A load shed module is provided in accordance with a presently preferred embodiment of the invention for use in a power distribution system that includes facility for delivering both electrical power and electrical power rate information from a utility supplier. The load shed module includes first connection capability to receive utility power and second connection capability for connection to a power load. An electrical switch such as a relay selectively electrically connects the first connector to the second connector to deliver electrical power to the load coupled to the second connector. A rotary switch is provided, and rate tier indicia is provided adjacent to the rotary switch and coordinated with position of the rotary switch for operator selection of a rate tier at which the second connection is to be disconnected from the first connector. Utility power rate information is received from the utility supplier and compared with the rate tier selected by the operator at the rotary switch. When the power rate information equals or exceeds the selected rate tier, the module second connector is disconnected from the first connector so that the associated load is effectively disconnected from the power distribution system.
In the presently preferred embodiment of the invention, which is specifically adapted for use in existing buildings, the module includes an enclosure on which the rotary switch and rate tier indicia are mounted. The first connector comprises a power plug that extends from the enclosure for receipt in a standard utility power outlet such as a wall socket, and the second connector comprises a power socket on the enclosure for receipt of a load power plug. The plug and socket are of standard configuration associated with power level--e.g., 120 VAC or 240 VAC. Alternatively, the module may be provided on a circuitboard or within an enclosure for placement on or within a wall adjacent to a building junction box, with leads extending for connection to power and load. The module may be employed for selective connection or disconnection of an entire circuit at the junction box. As another alternative, the module may be configured for placement in the wall, either at the time of building construction or as an aftermarket installation, in place of a conventional wall outlet.
In the preferred embodiment of the invention, the rate tier indicia and associated rotary switch positions are associated with a plurality of differing rate tiers, and one position of the rotary switch and the associated indicia are associated with continuous connection of the second connector to the first connector independent of power rate information. The power rate information in the preferred embodiment of the invention is received over the utility power lines using power line carrier or other suitable technology. As the rate information exceeds or falls below the tier threshold selected by the operator, the load is selectively disconnected or connected to the power system at random intervals to prevent massive connection or disconnection of loads from the power grid as the rate information fluctuates.
In accordance with another important aspect of the invention. voltage available from the power grid is continuously monitored, and the load is selectively disconnected from the power grid when available voltage is less than or greater than thresholds that might cause damage to the load. Voltage, current and phase angle are all monitored for calculating power and energy consumption. Energy consumption information and status information may be selectively transmitted from the module to the utility power supplier. The module in accordance with the present invention also monitors the quality of available power, and transmits appropriate information to the utility supplier.